Date of Award
Doctor of Philosophy (PhD)
Civil & Environmental Engineering
Short-cut nitrogen removal avoids nitrite oxidation to nitrate by nitrite oxidizing bacteria (NOB) and allows a) reduction of formed nitrite to nitrogen gas via heterotrophic denitrification and/or b) oxidation of remaining ammonia with formed nitrite to nitrogen gas via anaerobic ammonia oxidation (anammox). The precondition for achieving shortcut nitrogen removal is suppression of NOB, which is favored by warm and high ammonia strength conditions found in internally generated ammonia-rich waste streams through anaerobic digestion of waste solids referred to as sidestreams or reject water. The discovery of anammox bacteria in the mid-1990s, which are capable of transforming NH4+ to nitrogen gas utilizing NO2- as a substrate, has made suppression of NOB even more critical for nitrogen removal processes that take advantage of the lower energy and cost requirements of this nitrogen conversion compared to traditional nitrogen removal processes. Deammonification relies on ammonia oxidizing bacteria (AOB) to partially convert NH4+ to NO2- and anammox bacteria (AMX) to convert the remaining NH4+ and NO2- to nitrogen gas. The challenges of retaining slow growing AMX initially limited the expansion of benefits from autotrophic nitrogen removal; however, granular sludge and attached growth systems have proven highly effective in achieving deammonification in sidestream processes. Owing to the benefits that include energy and chemical savings, short-cut nitrogen removal has emerged as a viable technology for sidestream treatment. Consequently, mechanisms of NOB suppression to perform short-cut nitrogen removal are generally quite well understood for sidestream applications, which has allowed for the development of robust process control strategies. To date, the concept of deammonification has successfully been implemented in 100 full-scale treatment facilities treating high ammonia strength waste streams around the world.
Due to the success of sidestream short-cut nitrogen removal systems, there is great interest in applying this form of nitrogen removal to mainstream processes. Since the dilute and cold conditions of mainstream are not well-suited for suppression of NOB, short-cut nitrogen removal, in particular deammonification, has yet to be implemented in full-scale. The successful implementation of mainstream deammonification would revolutionize and disrupt the way in which biological nitrogen removal is achieved at wastewater treatment facilities. It represents a paradigm shift for the industry, offering the opportunity for sustainable wastewater treatment, energy neutral or even energy positive facilities and dramatic reductions in treatment costs, which has widespread environmental, economic and societal benefits.
This dissertation deals with the pilot-scale investigation of short-cut nitrogen removal in low ammonia strength wastewater with temperatures <25 >°C. An A-B process pilot-scale system was operated over a two year period. The A-stage was a high-rate activated sludge system for carbon removal and the B-stage consisted of an activated sludge system that targeted NOB out-selection which was followed by a fully anoxic anammox MBBR. In this study, by employing a combination of intermittent aeration, high DO (>1.5 mg/L), residual effluent NH4+ (>2 mg/L), and aggressive SRT (< 5 days at 23-25 °C) and HRT (< 4hr), NOB out-selection was achieved in the continuous-flow activated sludge process. The development of novel aeration and SRT control strategies based on advanced instrumentation, control, and automation for achieving NOB out-selection in an activated sludge process and nitrogen polishing in subsequent anammox MBBR was shown. A very fast startup time (less than 2 weeks) for anammox MBBR was achieved by seeding anammox granules obtained from a full-scale, sidestream anammox treatment process. Anammox MBBR proved highly stable during the study and a very high maximum nitrogen conversion rate (> 1 gN/m2/d) was demonstrated. Therefore, this study shows carbon re-direction (potentially for energy production) in a high rate A-stage does not cause carbon limitation in the B-stage for nitrogen removal if control strategies and anammox-based nitrogen polishing is used as investigated in this study.
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Regmi, Pusker R..
"Feasibility of Mainstream Nitrite Oxidizing Bacteria Out-Selection and Anammox Polishing for Enhanced Nitrogen Removal"
(2014). Doctor of Philosophy (PhD), Dissertation, Civil & Environmental Engineering, Old Dominion University, DOI: 10.25777/78fk-ef25